This invention generally relates to a laser apparatus. For example, this invention specifically relates to a laser apparatus usable in an exposure system.
During the manufacture of large-scale integrated circuits, photolithography processes are used in printing patterns on semiconductor wafers. The photolithography processes are generally performed via exposure systems. Lasers are frequently used as light sources of the exposure systems. The manufacture of very large-scale integrated circuits requires shorter-wavelength light sources. Excimer lasers are applicable to such light sources.
Generally, an excimer laser using an optical resonator generates an oscillation line having a half-width of about 0.5 nm. To use such an excimer laser in the manufacture of very large-scale integrated circuits, it is necessary to decrease the half-width of its oscillation line to about 0.005 nm or less. The decrease in the width of the excimer laser oscillation line is conventionally realized by wavelength selectors such as a prism, a diffraction grating, or a Fabry-Perot etalon. These wavelength selectors are sensitive to temperature and pressure, so that changes in the temperature or pressure cause considerable variations in the selected wavelength. It is important to stabilize the wavelength of the light of the exposure system during the manufacture of very large-scale integrated circuits.